Robert Watson writes: > > On Tue, 1 Aug 2006, Andrew Gallatin wrote: > > > > - The ifnet send queue is a separately locked object from the device > > > driver, > > > meaning that for a single enqueue/dequeue pair, we pay an extra four > > > lock > > > operations (two for insert, two for remove) per packet. > > > > Going forward, especially now that we support sun4v CoolThreads hardware, > > we're going to want to rethink the "single lock" per transmit routine > > model > > that most drivers have. The most expensive operation in transmit routines > > is bus_dmamap_load_mbuf_sg(), especially when there is an IOMMU involved > > (like on CoolThreads machines) and there is no reason why this needs to be > > called with a driver's transmit lock held. I have hard data (from > > Solaris) > > about how much fine grained locking in a 10GbE driver's transmit routine > > helps. > > Right now, with the exception of locking for the ifnet dispatch queue, I > believe our ifnet API pretty much leaves decisions about the nature and > granularity of synchronization to the device driver author. The ifnet queue > is high on my list to address (hence this thread) -- are there any other > parts > of our device driver framework that stand in the way from a device driver > being modified to support greater parallelism in sending?
No, not that is directly related to ethernet drivers. However, busdma is a pain. Specifically, I hate that bus_dmamap_load_mbuf_sg() requires a bus_dmamap_t. That means that any fine-grained driver will need to "allocate" a bus_dmamap_t either via bus_dmamap_create(), or by pulling a pre-allocated bus_dmamap_t from a pre-allocated pool. Either will require a lock. Solaris has a similar problem, and I use the pool approach in my Solaris driver. Linux's pci_map_single()/pci_unmap_addr_set()/pci_unmap_len_set() is just so much nicer to use... Drew _______________________________________________ freebsd-net@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "[EMAIL PROTECTED]"
